This invention relates generally to combustors used in gas turbine engines and in particular to a low emissions combustor that burns gaseous fuel.
Air pollution concerns worldwide have led to stricter emissions standards requiring significant reductions in gas turbine pollutant emissions for both industrial and power generation applications burning either liquid or gaseous fuel.
Sjunnesson et al, International Publication No. WO 96/02796 discloses a low-emission combustor for a gas turbine engine having an outer casing with an upstream end wall with a pilot fuel injector, a first radial flow swirler, an igniter for initiating a stable diffusion frame in a pilot zone, a second coaxial swirler, main fuel injectors, secondary air inlets, and a main combustion zone. Importantly, the pilot zone is confined radially outwardly by a surrounding wall which constitutes the radially inner confinement of an axial outlet portion of a radial vaporization channel extending from the second swirler and a third radial flow swirler is adapted to supply the secondary air in a rotary motion opposite to that of the main flow of fuel and air.
One disadvantage with having a confined or recessed pilot zone is that the walls surrounding the zone are exposed to very high temperatures and as a consequence need to be cooled. Typically, cooling air from other parts of the gas turbine engine are brought to these walls for this purpose. However, the extraction of the cooling air from the engine results in a reduction in the engine""s performance, increases carbon monoxide emissions and produces inferior engine operability and starting. Another disadvantage to the combustor disclosed in the ""050 patent is that it requires three radial swirlers which adds expense and complexity to the design. Prior examples of combustors, therefore, are not as economical and robust as desired for use in small power generation systems.
Accordingly, there is a need for a low emissions natural gas combustor that does not have a confined pilot zone and is a simpler and more economic design than prior combustor designs.
The present invention provides a combustor dome for use in a combustor having an igniter mounted in a central bore. Moving outward from the bore is a concentric pilot fuel passageway having an outlet with a plurality of holes for expelling the pilot fuel at an outward angle away from the igniter tip. Concentric about pilot fuel passageway is an air passageway that has an outlet with a nozzle. Lastly, concentric about the air passageway is a premix passageway. The outlets of the pilot fuel passageway, the air passageway, and the premix passageway are all approximately coplanar.